Field of the Invention
The invention relates to the field of laser imagesetters and, in particular, to their tuning for the purpose of optimizing the image quality of a photosensitive material that is illuminated in a laser imagesetter and is subsequently developed, in particular, during illumination tests, in the event of a change between different photosensitive materials or in the event of a variation in their properties.
The tuning of commercially available laser imagesetters to the photosensitive material to be illuminated, for example, films, pieces of paper, or printing plates, which usually needs to be carried out in the event of a change of the material or in the event of a change to its properties by the manufacturer, usually takes place with the aid of test illuminations. During these test illuminations, a particular test pattern is selected as a function of the material being used, and the photosensitive material is illuminated in the laser imagesetter with the test pattern, to evaluate it after developing, the criteria of the evaluation being different according to the material being used. For each of several possible imagesetter resolutions, a separate test run is carried out, during which the material being used is successively subjected to a filter test and a light test, to check by evaluating the developed test patterns whether or not optimum results can be obtained with the selected imagesetter adjustment. In addition, a focus test is carried out for each material to check the focus adjustment of the imagesetter with respect to the material being used.
Carrying out these test illuminations, however, takes a comparatively long time and entails a comparatively high workload. For instance, the time taken in the case of five possible imagesetter resolutions and an average duration of 10 minutes per test is almost 2 hours to carry out the 11 necessary tests (5 filter tests, 5 light tests, and 1 focus test). When two different materials are being used, for example, film and offset sheet, as many as 22 tests are necessary, and the time taken is, therefore, twice as long.
If the result of the test illuminations does not correspond to expectations, the test illuminations need to be carried out again after varying some of the imagesetter adjustments.
Variations in the imagesetterxe2x80x94materialxe2x80x94developing machine process chain, for example, batch-dependent variations of the photosensitive material or variations due to ageing of developer chemicals, can also make it necessary to repeat the test illuminations.
The test illuminations are usually carried out according to the specifications, for the photosensitive material respectively being used, from the manufacturer who, prior to a market release, determines the imagesetter adjustments that are most suitable as a standard and supplies these to the customer while citing the respective manufacturer reference. The manufacturer references used by different manufacturers, however, are of different types and do not contain any information about material-specific properties, such as material thickness and material sensitivity, which would permit the customer to derive illumination parameters tailored to his or her own requirement from them.
It is accordingly an object of the invention to provide a method for adjusting illumination parameters of a laser imagesetter that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that reduces the time taken and the workload for determining the correct imagesetter adjustment.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for adjusting variable illumination parameters of a laser imagesetter, including the steps of defining variable illumination parameters of the laser imagesetter including at least one of the group consisting of laser power, focus adjustment, scan rate, and feed rate, adjusting the illumination parameters of the laser imagesetter during illumination tests of a photosensitive material by calculating at least some of the illumination parameters prior to the adjustment based upon imagesetter-independent characteristic data selected from at least one of the group consisting of material thickness, material sensitivity, material-specific test patterns, and material-specific evaluation criteria of the photosensitive material to be illuminated, and subsequently automatically adjusting the calculated illumination parameters.
According to a first aspect of the invention, at least some of the illumination parameters are calculated, prior to the adjustment, based upon imagesetter-independent characteristic data including material thickness, material sensitivity, material-specific test patterns, and/or material-specific evaluation criteria of the photosensitive material to be illuminated.
This aspect of the invention is based on the idea of replacing the instructions for carrying out the test illuminations by imagesetter-independent material-specific characteristic data, which are used as a basis for calculating suitable illumination parameters as well as for automating an illumination process and, in particular, test illuminations by corresponding automatic control of the laser imagesetter based upon the calculated illumination parameters.
The term imagesetter-independent characteristic data refers to material-specific data such as material thickness, material sensitivity, material-specific test patterns, and/or material-specific evaluation criteria, which can be given without reference to a particular laser imagesetter, although these characteristic data may also include data such as an imagesetter resolution, if this material-specific imagesetter resolution is suitable for arbitrary laser imagesetters.
From the imagesetter-independent characteristic data, the imagesetter-specific illumination parameters are, then, calculated in a particular laser imagesetter, or in a computer connected to it; besides the imagesetter-independent characteristic data, imagesetter-specific characteristic data, for example, laser-diode current, laser-diode power, filters, or shutters, also have an influence in the calculation.
The imagesetter-independent characteristic data are advantageously stored on a data medium, for example, a CD-ROM or a floppy disk, which can be read by the laser imagesetter or by a computer connected to the laser imagesetter, or they may be called up by the customer directly through data lines, for example, over the Internet from a homepage of the manufacturer of the imagesetter or of the photosensitive material. Taken together, the imagesetter-independent characteristic data of a material to be illuminated will be referred to below as material drivers, by analogy with corresponding terms in the computer sector.
To permit fast processing of the characteristic data, in accordance with another mode of the invention, prior to the illumination of a photosensitive material, suitable illumination parameters such as laser power, focus adjustment, scan rate, and/or feed rate be calculated by a processor integrated in the laser imagesetter, or a processor of a computer connected to the laser imagesetter, from its material drivers by using predetermined algorithms; the algorithm for calculating the laser power contains, as a variable, at least the material sensitivity, expressed as an energy density, and advantageously furthermore an imagesetter resolution that is suitable for the material and a scan rate that is dependent on the imagesetter resolution, while the algorithm for calculating the focus adjustment contains at least the material thickness as a variable.
In accordance with a further mode of the invention, advantageously, the calculation of the focus adjustment begins from a reference focal point, which has been determined beforehand at a defined temperature for a reference material with a defined material thickness; the algorithm for calculating the focus adjustment contains, as a variable, the difference between the material thickness of the photosensitive material to be illuminated and the defined material thickness, as well as a difference, if there is one, between the defined temperature and a temperature prevailing during the illumination.
To permit fast access to the material drivers in the event of a change between different photosensitive materials, in accordance with an added mode of the invention, it is proposed that a plurality of material drivers be stored as a database in an internal memory of the laser imagesetter, or in a memory of a computer connected to it, from where a required material driver will be called up by a utility or management program, which will be referred to below as a material manager by analogy with a corresponding term in the computer sector. To simplify the calling up of the material drivers, each of the plurality of photosensitive materials in the database is advantageously provided with an address, which can be accessed by inputting a manufacturer code and a material code so that confusion between similar material codes of different manufacturers can be avoided. The manufacturer and material codes may, for example, be input on a control panel of the imagesetter, by a keyboard or a mouse pointer on a screen interface of the computer, or by a barcode reader, which is used to read barcodes applied to the photosensitive material itself to avoid confusion.
In accordance with an additional mode of the invention, there is provided the step of selecting from databases characteristic data of the respective photosensitive material to be illuminated with the imagesetter-independent characteristic data of a plurality of photosensitive materials.
In accordance with yet another mode of the invention, there is provided the step of providing each of the plurality of photosensitive materials in the database with an identifier.
In accordance with yet a further mode of the invention, there are provided the steps of storing the database with the imagesetter-independent characteristic data in a memory of one of the imagesetter and of a computer connected to the imagesetter and reading out the associated characteristic data and transferring the associated characteristic data to the processor to calculate the illumination parameters when one of the identifiers is input.
With the objects of the invention in view, there is also provided a method for adjusting variable illumination parameters of a laser imagesetter, including the steps of defining variable illumination parameters of the laser imagesetter including at least one of the group consisting of laser power, focus adjustment, scan rate, and feed rate, adjusting the illumination parameters of the laser imagesetter during illumination tests of a photosensitive material by calculating at least some of the illumination parameters prior to the adjustment based upon imagesetter-independent characteristic data selected from at least one of the group consisting of material thickness, material sensitivity, material-specific test patterns, and material-specific evaluation criteria of the photosensitive material to be illuminated, subsequently automatically adjusting the calculated illumination parameters, successively illuminating the photosensitive material in the course of a single illumination test with a plurality of laser-power levels of the imagesetter to determine the laser power, an increment of the laser power between two adjacent laser-power levels being constant on a logarithmic power scale, and developing and evaluating the illuminated material following the illumination test to determine a most suitable laser-power level.
For photosensitive materials with unknown characteristic data, the illumination parameters to be adjusted may be determined by illumination tests, the number of which can be reduced if, in accordance with yet an added mode of the invention, the necessary laser power is determined by successively illuminating the photosensitive material in the course of a single illumination test with a plurality of laser-power levels of the imagesetter, the increment of the laser power between two adjacent laser-power levels being constant on a logarithmic power scale, and by developing and evaluating the illuminated material following the illumination test.
Furthermore, in the case of a plurality of possible imagesetter resolutions, the number of test illuminations can be reduced to one if, in accordance with yet an additional mode of the invention, the laser imagesetter is analyzed over the entire range of its possible adjustments during the initialization phase, the laser power for a first imagesetter resolution is selected according to the manufacturer""s information or from experience, and the laser powers for the further imagesetter resolutions are mathematically calculated and adjusted by using this as a basis, while taking the results obtained during the analysis into account.
With the objects of the invention in view, there is also provided a method for adjusting variable illumination parameters of a laser imagesetter, including the steps of defining variable illumination parameters of the laser imagesetter including at least one of the group consisting of laser power, focus adjustment, scan rate, and feed rate, adjusting the illumination parameters of the laser imagesetter during illumination tests of a photosensitive material by calculating at least some of the illumination parameters prior to the adjustment based upon imagesetter-independent characteristic data selected from at least one of the group consisting of material thickness, material sensitivity, material-specific test patterns, and material-specific evaluation criteria of the photosensitive material to be illuminated, subsequently automatically adjusting the calculated illumination parameters, illuminating the photosensitive material with a material-specific test pattern simultaneously developed during subsequent developing of the material in a developer, subsequently evaluating the simultaneously developed test pattern, and automatically varying some of illumination parameters and process parameters of the developer as a function of a result of the evaluation.
Because the process of illuminating the photosensitive material may be subject to variations, for example, due to a decrease in the laser power of the laser imagesetter, in accordance with again another mode of the invention, it is proposes that the illuminated photosensitive material be developed to make a test pattern, that the test pattern subsequently be evaluated, and, as a function of the results of the evaluation, that some or all of the illumination parameters be varied automatically if appropriate. Advantageously, the evaluation takes place by a measuring instrument, for example, by a densitometer, which measures the difference between an actual value of the optical density of the test pattern that is generated and a predetermined setpoint value. A correction value is subsequently calculated from the measured difference, and it is, likewise, included as a variable in one or more of the algorithms used for calculating the illumination parameters.
Expediently, one of the illumination parameters is selected as a guide value, for example, the value of the energy density in the developer, and its calculation includes, as a variable, the correction value determined during the evaluation of the test pattern, while the other illumination parameters are varied according to a predetermined relationship in the event of a variation of the guide value.
Because variations may also be induced by effects within the developing process, for example, due to ageing of developer chemicals in a developing machine connected downstream of the imagesetter, and because it may not necessarily be possible to compensate for these effects by correcting the illumination parameters in the imagesetter. In accordance with again a further mode of the invention, it is proposed that the correction value determined during the evaluation of the test pattern be employed alternatively or additionally to regulate the developing process in the developing machine.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for adjusting illumination parameters of a laser imagesetter, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.